<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>
    var a = 'username';

    var o = {
        'user name':'frank'
    };
    console.log(o['user name']); //只能采用第二种方式




</script>
</body>
</html>